In the laser micro-precision machining for semiconductors such as LED wafer and the like, the sapphire substrate to be used is usually a wafer with a c-plane. As illustrated in FIG. 1, during a laser dicing process of the LED wafer, the whole piece of circular wafer needs to be split into a plurality of single core particles with rectangular shape. Two mutually perpendicular dicing directions are generally corresponding to an a-plane and an m-plane of the sapphire crystal, and the a-plane and the m-plane are both perpendicular to the c-plane. Since the m-plane is close to the r-plane (cleavage plane), and the r-plane is not perpendicular to the c-plane and forms a certain inclination angle with the c-plane, the single final core particle will actually be cracked along the r-plane after laser dicing, such that there is a certain deviation between the laser machining point corresponding to the CCD (charge-coupled device) camera and the actual cracking position of the wafer, thus causing the actual crack to deviate from the intermediate position of the dicing path. When the dicing path has a greater width, the actual crack does not extend into the emitting electrode region (electrode) of the chip. However, during the actual process, in order to increase production as much as possible, the width of the dicing path becomes increasingly smaller. If the crack deviates from the intermediate position of the dicing path, the emitting electrode region of the chip will be scratched, thereby affecting the final yield.